Other cultures, countries and religions have a completely different date (muslims 1434, jews 5773, myself since I was born...) This is a world currency, and also the date is not very important.
So it would be much nicer that in case of using a date, use the number 4 or 5, I'm not sure, but since the genesis block was created, or since bitcoin started, for example. This way you don't offend anyone, otherwise yours will be a coin "for christians only".
Not to forget that we are currently living in
the year 102 of the Republic of China... with "Republic of China" referring to the tiny yet democratic island of Taiwan by the way, not to be mixed up with the giant communist thingy called by almost the same name, only with an added "People's". Which uses 2013. And by a freak chance it is also
the year 102 in North Korea, simply by the coincidence of Kim Il Sung's birth having been in 1912, where in China the new era of the republic had started (and lasted till 1949,when the communists had won the civil war aka the next revolution). Oh, and the
Japanese Taisho period also had the same numbering of years.
Which leads me to my point, finally: since the creator(s) of Bitcoin chose a Japanese pseudonym, numbering years in Japanese ways might be a way to honor this aspect of Bitcoin's "birth". Similar to the Chinese, to my understanding
Japanese traditionally counted years from the start of a new era. This era in our case could be the start of the Bitcoin network in 2009. Of course this obvious counting method has already been suggested. I am simply trying to point out one possible reason supporting this kind of counting.
To identify the era name, obvious choices would be Satoshi, Nakamoto or Bitcoin. So the current year could be called S5, N5 or B5.
A reason for not using S5 could be that it could refer to year 5 of the Showa period (1930). In this period the then militaristic Japan caused huge grief and suffering throughout Asia.
A reason for not using S5 or N5 would be that Japanese era names are not referring to the names of the respective emperors or events, but to a description of that era.
So B5 would be one possible choice in my opinion. Or if you want to go all Japanese style, ビットコイン5... or even replace the "5" by Japanese/Chinese numerals, resulting in ビットコイン五 - although probably most Westerners without Chinese/Japanese reading skills could not identify the numeral, except probably those few who
play Mahjong and recognize the numbers from the WAN tiles 
